The availability of the white LED (light emitting diode) die in high power versions, e.g., 1 watt (W) or more electrical power, has enabled the production of lamps with several hundred to several thousand lumens (lm) of light output. The 60 W incandescent bulb produces approximately 800 lumens of output, so a 110 lumen per watt plurality of white 1 watt LEDs would need 850/110 or 8 LEDs, with 8 watts of power (1 watt per LED) producing 880 lumens of light output at the emitter (LED). Due to lightpath losses, typically 90% of that light is useful, resulting in approximately 800 lumens of net light output in the instant example.
Since the LED is a planar light source in the near field, it cannot produce an omnidirectional cylindrical light output in the near field like a suspended filament can, typically producing a Lambertian beam pattern with a half power inscribed beam angle of 120 degrees, possibly assisted by an integrated silicone dome, though the beam angle can be varied by the LED component manufacturer by design.
So, to emulate a piece of suspended wire, heated by an electrical current, the first consideration of sufficient light output is addressed by using 8 LEDs in the instant example. Those eight LEDs, in this example, each only produce a fractional portion of the cylinder or sphere of light produced by the filament, so they could be arranged to produce a similar light pattern to the incandescent. Then, being a two port device, a diode, each LED must have two electrical connections made to it. Each LED has a forward voltage of about 3V (volts) per LED, so placing them in series means about 24V DC (direct current) of forward voltage on the “array”. In one embodiment, the line voltage is nominally 120V AC (alternating current) RMS (root mean square)+/−10%, so it can be as high as 132V RMS, or 187V peak. So a plurality of DC LEDs needs some means of changing AC to DC, as well as lowering the voltage to the nominal 24 VDC or so. The sensitivity of light output to voltage on LEDs is very high, so they are typically controlled by the lower sensitivity current through them, resulting, in the instant example, in 24 VDC or so across the 8 LEDs.
A power conversion apparatus is typically used to convert the 120 VAC RMS line voltage into current through the LEDs. The mathematical product of forward voltage and current for an LED is the power applied to the device. Of that power, about 80% is produced as heat and 20% as light. A power conversion block may be about 80% efficient, so thermal power that must be removed, and dumped into the ambient air by means of natural or forced convection, after conducting the heat away from the high density heat flux at the devices is going to be about 8.4 watts. If we factor in the power conversion block, and because of the power converter losses, 10 W of line power must be delivered to the power converter in order for it to deliver 8 W of electrical power to the LEDs in the instant example. The device, known as a ‘heatsink”, for moving (“sinking”) the heat away from each individual LED by thermal conduction and providing the surface area for convection cooling is, in LED lamps’ prior art, typically comprised of relatively thick, diecast, aluminum and is typically designed to maximize material cross-section to enhance the thermal conduction process and in many instances is finned to increase the surface area of the device to enhance convective/radiative heat transfer from the heatsink to ambient air (the “sink”). An aluminum circuit board core (“MPCB”) may be attached to the heatsink, where the MPCB forms an electrically interconnected sub-assembly. Some implementations actually use an air-mover (fan, as an example) to enhance the convection portion of the heat transfer process. The entire configuration, with all these considerations, is designed to more or less fit into the ANSI A19 specification light bulb envelope using North America as an example, in the case of the 60 W standard service light bulb. Known prior art implements three dimensional, rotations of a profile in cylindrical coordinates, and few, if any are known to be the point sources of light that distribute light evenly in all directions to result in the same light flux on a spherical surface a constant distance from that point (or, short, line) source location specified by ANSI's A19 specification. A line source may also be used instead of a point source where there is a linear arrangement of a plurality of interconnected LEDs, which will result in a cylindrical distribution of light in the near field. To further complicate matters, this standard service A19 lamp is used horizontally, usually in pairs, in ceiling fixtures where half the emitted light goes upwards to the ceiling and a near-perfect reflector is rarely used to reflect the light out of the fixture down into the room. These fixtures are usually fully enclosed, so in the case of the incandescent, 120 W of heat source is fully enclosed within the fixture, with a very poor thermal conductivity glass cover providing optical transmission and a degree of dustproofing. Some implementations of LED lamps are as shown in the following figures.
FIG. 1 is a view of a Mirabella™ compact fluorescent lamp (CFL). FIG. 2 is a view of a Cree™ LED A19 beside an incandescent A19. FIG. 3 is a view of the interior of the Cree™ bulb showing the LED arrangement on an aluminum carrier attached to a heatsink, and the use of a connector “clip” which then attaches via a connector to the driver circuit board. FIG. 4 is a further view of the interior of the Cree™ bulb. FIG. 5 is a view of an EcoSmart™ bulb showing an alumina LED board mounted in an aluminum heatsink, with external wiring going down inside to the driver board housed inside the heatsink/base. FIG. 6 is a view of a Best Buy™ 60 W bulb, which has three aluminum heatsinks to which aluminum substrates are screwed, then these are wired into the base where the driver circuit boards are. A translucent plastic shell is used between the aluminum heatsink “petals”, and such shells are typically attached with an adhesive. FIG. 7 is a further view of the Best Buy™ 60 W bulb, showing its interior. FIG. 8 is a view of an LG™ “snocone”, which uses a similar design as the EcoSmart™ bulb. FIG. 9 is a view of an LED bulb from TESS Corp., which has multiple intense LED sources, two of these output 429 lumens at 8.6 W. FIG. 10 is a view of a Maxxima™ LED bulb. FIG. 11 is a view of a Phillips™ LED bulb, from blog.makezine.com. The aluminum core LED carrier board has a connector, which screws to the large heatsink. Also shown are a white plastic reflector and a remote phosphor (yellow) plastic cover. FIG. 12 shows the circuit board of FIG. 10, with a driver, which slides inside the aluminum heatsink and connect via soldered wire to the screw caps and connectors to the LED sectors.
Significant costs are incurred in conventional LED lamp designs, as can be seen in the examples, by the use of large die-cast aluminum heat sinks (16%), labor and assembly, connectors, clips, screw base, and hand soldering of the screw base and wires between the driver board and the LED aluminum core circuit board (18%). Lifetime claims of tens of thousands of hours are contraindicated by the extensive use of connectors and hand soldered joints that can and will fail especially during such conditions as temperature cycling or extended high temperature operation and of voiding within thermal compounds between aluminum core boards and the main aluminum heat sink. See for example, FIG. 13, which is a cutaway view of a 3M™ LED bulb.
The nature of design practice among those versed in the art is, as shown in the above examples, to use a screw base, a cast aluminum heat sink, a driver circuit board or boards made of material such as FR1, CEM-3, or FR-4, connectors or solder joints to an aluminum-core circuit board sub assembly, which is then mechanically attached using thermal compounds and fasteners to the aluminum heat sink. A plastic shell is used for such purposes as to diffuse light, convert blue light to white light, to protect components within the shell, to preclude a shock hazard, or in 3M's case guide light, with the light originating from the individual LED sources in a singular or plurality of arranged LEDs, with every design shown above exhibiting a compromise to ideally having an omnidirectional point light source, or short vertical line source, as required in both the ANSI A19 specifications and as inherent in incandescent light bulb designs. All LED lighting (as shown above) that attempts to replace A19 light bulbs adheres to a geometric rotation of one or more silhouettes in a cylindrical coordinate system about a vertical centerline and all attempt to arrange the LEDs in a compromise between such things as optical, thermal, reliability, manufacturing, safety, and electrical considerations. All attempt to couple as much of the LEDs' heat to the large diecast heat sink for exchanging the heat to ambient air via convection, conduction, and radiation. Electrical connections shown above are always made using a metal “Edison screw” cap in the instance of a North American A19 bulb, though other means such as a bayonet or other means of termination are not precluded.
Some of the resulting light patterns from various A19 replacement designs are shown here. FIG. 14 is a light pattern for an A19 replacement LED bulb by Cree™. FIG. 15 is a light pattern for an A19 replacement LED “Lighting Science” bulb by EcoSmart™. FIG. 16 is a light pattern for an A19 replacement LED Maxxima “snocone” style bulb. FIG. 17 is a light pattern for an A19 replacement compact fluorescent lamp by Mirabella.
Therefore, there is a need in the art for a solution which overcomes the drawbacks described above.